This is an idea that literally just popped in my head, how do people keep moisture out of there enclosures?
I know the best thing is to have a properly seleaded housing but that becomes a trouble when ventilation is needed.
I actually quite like the idea of these solid state dehumidifiers:

Moisture/humidity generally isn't a huge problem. When the humidity is high and temperature is low and condensing occurs is when there is a potential problem.
That's a cool device in the video. I had no idea such a thing existed.

I am in south-east Queensland and have high humidity to contend with.
I have never had an issue with condensation in my control boxes.
They have a vent down the bottom and a fan assistedvent at the top.
What a neat device in the video. I too did not know they were available

In Port Hedland when working with control gear we had issues (not christmas light related), but we used the moisture bags you get in packaging. You can buy them in bulk off ebay or i think even jaycar sell them. One bag left in the box "just in case" always protected our electronics. We swapped them out every 6 months. Beginning and end of wet season basically.

generally you will find the heat from the power supply or controller will be enough to stop any condensation while running, general humidity in itself should not be a problem. If you leave the power on and just in standby while the show is not running, I would imagine it should take care of itself, worst case add a fan and that will stop any condensation from being able to form.
I worked in the tv repair industry in Darwin for 5 years back in the 80's wet season was always above 90% humidity. The electronics was never an issue in tv's or videos. It was the metal bits like the frame etc that rusted. The electronics is made from better stuff and I never saw a problem.